The filming was done by Sam Hardie with editing by Alejandro Acin. The filming was all done handheld on a Sony and is absolutely beautiful. It's 50mm 1.4 wide open dreamy and nostalgic and when I first saw the film I was transported into this strange dreamland somewhere between the past and the present.

Isabel's voice accentuates that dreaminess. I remember watching it and thinking 'well, it's beautiful, but maybe it's too beautiful. How does it connect to the book'.

But then I looked again and saw what Sam had been filming all the way through; the light flickering through the trees, the shade of leaves dappled against Isabel's skin. Sam filmed through trees, through shrubs, through the flowers of the invasive species that fill the land surrounding the BMX track.

The beauty isn't coming from the actual places. All of the places we filmed, all of the places in the book are of a type. They are not pastoral landscapes, they are not wilderness landscapes, they are not sublime landscapes, they are completely beat-up post-industrial/post-agricultural landscapes.

But they are outside and there are trees, flowers, leaves and the sights and smells of vegetation growing from the land. There's the smell of the earth, there's the touch of the wind, there's the sense of being in nature, however messy it might be. And it is messy.

The Japanese have this idea of 'forest-bathing' - shinrin-yoku. It's the idea that you go to the forest to bathe your senses in the sights, the sounds, the smells, the touch - and even the taste - and that reduces stress, develops your immune system and does all kinds of other things. Because just as you smell and taste the diesel on your tongue when you're in the city, so you smell and taste the resin, the pollen, the dust when you're in the forest. But where urban particulates kill, arboreal particulates make you flourish. It's the same if you work on a garden or allotment - it boosts your immune system, lowers your heart rate and makes you a better person all round.

Forest-bathing is an antidote to being indoors. It is also calming, it's meditative, it relaxes you. By being outside where there is flora, your brain is taken down a couple of notches. When you're inside your mind is always occupied, not just by the drudgery of everyday existence, but also visually by the grids that dominate our domestic interiors. Everything is more or less ordered. There are straight lines, there are diagonals, there are angles, there are frames. It's the same when we look at a screen - everything is ordered. This ordering means our eyes never get a rest. They are always on the look out for regular patterns and because that is all you have inside, the eyes never stop. And because the eyes never stop, the brain never stops.

Go outside and look at a tree and the picture changes. The shifting leaves are a mass of information, a continually changing pattern of light and shade, of geometric patterns that never quite form a clearly defined shape. It's too much information for the visual cortex to handle, so instead of keeping on working, it simply stops. It's visual overload. It shuts down and then you can rest.

It's also something universal. I remember going to Westonbirt Arboretum with a group of Somali students. It was one of the most touching moments when they all suddenly started looking around what I thought was this incredibly English garden with a sense of joyful nostalgia. The sense of elation combined with calmness was palpable. They all had a nostalgia for the landscapes they grew up in or visited at the weekend. It was a kind of muscle memory of relaxation and it reminded them of home, which was something I found touching but also surprising and revealing of my ignorance.

They were so used to living in the heart of the city and not getting out too much that by the time they got to Westonbirt, to countryside, they were quite overwhelmed. Not by the sight, but by the feeling. Westonbirt reminded them of home! It was something they remembered and something they deserved.

Earlier in the week I wrote about Mathieu Asselin and his book Monsanto. He talked about it at the symposium on photography, politics and change at Gazebook Sicily. He said there is no place for ambiguity in the current political climate, or maybe in any political climate. I'm with him on that. Because I talked about All Quiet on the Home Front at the symposium, and how the personal message can convey something political. I also said that I didn't think that photography could effect change, or not All Quiet on the Home Front.

But maybe I was too hasty. Isabel grew up with these amazing environments on her doorstep and they are what helped make her what she is today. But doesn't everyone deserve the same chance. Shouldn't the essential nature of open, green spaces be recognised for the benefits it provides, shouldn't the cleansing powers of trees and shrubs be available to everybody. For my former students it's not available. Landscape is power after all and in Bristol where they live, in the UK as a whole, the talk is not of providing more green spaces, but of cutting back on green spaces, of removing trees, of making the urban environment even more barren and hostile, because caring for trees, creating a natural environment costs money. And that, with no hint of ambiguity whatsoever, is wrong!